Antenna



G. H. BROWN Dec. 7, 1948.

ANTENNAy Filed Aug. 12, 1944 I VEN TOR. ylrowm Innen-Wire transmissionlines.

Patented Dec. 7, 1948 Grenrge lilrown, 'Princeton-N. J., assiale 'to.Radin4Corfporaticm,l of America., Aia corporation:

` of. Delaware Y y invention `relates rto 'radio yantennas and hasiorz-its'principal object Athe provisionfomeans Iorepreuenting directfeed-tlnough of .radiofreen'sleiueyv energy from one antennatoanothernear- .byfantenna c certain typesof radio reliectionrobjectydetecting-systems, signals are radiated- .from 4one antenna ,andylcrckecl .up by 'another antenna after 'neallection ,-by :an object. Inysuch systems it `is generally highly desirable to.rninirnize 'or pre'-Vent the transmissiomorenergy directlyiromrone oxiithecantennasz'tothefother without reflection from the i'obj'ect, :thesame time',` .the.antennas must. be plfaced' .relatively near -to reach. other.Groundedslrietds. interposed-'between the: time antennas have. beenfound to be.v Aineiective, par- 'ticularlyzatitthe higher frequencies,because four'- re'nts'induced .in the 'shields by ytime 2transmittin2,rantenna .cause 'they shields'to. reradiate; Thu-s the shield tend'stofunction merely as: av coupling.. .1e-le'- ment...=between. the twoantennas. 1n accordance with the present invention, the ttwo'ant'ennas;are isolated from each other byxshslel'ds 'consti-'noted toi form:zarplurality of shortcircuitedquarter-Wave As is `Well' lmnwfn toit-hoseskilled in the art, .a short-circuited'trans.- missionV line presentssubstantially i'nni'te. :im-- pedance to the: flow of current at thefrequencyzat which the line-is off-'one-quarter Wavelength. 'The instantinvention utilizes. this phenomenon lby placing '1a .plurality oi' suchlinesqiny ,pcsitinnsgsucli as to prevent the-.flaw of currents which`tend to cause Mie-transfer of energy from one. antenna to tire-ether. vv

1 The invention will' be described Withreference scribedlfabove. Each ofthe'antennasisfd'irective, f

and :c'omprisesa .di-pole, l locatedzat. thefocus of a;..eylindrical1parabolicf reflector 3..' Each ,of the neectors :3 .is provided withside walls; 5 fand." 1;. Inrthe-absence'of :any further shieldingmeansyb'ertween the dipoles I, energizationso. the antenna.

A Wi1lind1-1ce-currents ,in its side Walls- Tliese vcurrents lWil-llin-y turn. induce currents in the side walls', 5- ofthce antenna B,causing radiation theretreintathe-dipoley I of the -antennailv .-fllopneitentthe. above-descrlbed couplingfacf nciaims. (c1. 25o-esi tionfrom taking; place, .a plurality :ci .nat plates 9 of conductivematerial are placed between the antennas .A .and ;-B with each.:connected y :at l,one of its edges to a conductive sheet tt yextendingirom V`tlfie-giilallfil; ofthe antenna A, parallel tothe line betweenthe antennas, to theA wall. 5 oi the famiennaflB-v.4 Thepplat-es1f9f-ategparalle-lto the Walls 5 and 1 and are spaced at intervals-ofapproximately one-tenth Wavelength at the frequency at which the `systemis .to operate. 'Each ci" vthe plates .9' extend's forwardly one-quarterwavelength'from its ,point oi" connection to 'the sheets Il... The wall.Toi the antenna A, together with the nearestof lthe plates 9', .actsasia quarter Wavelength. open- Wire line, short-circuited' at itsrearward end by the `sheet ll., thus .presentinga substaritiallyiilnnte.impedance between the'ior'- wand' edges of the Wall. "l and the firstplate 9; Silnilarly,.eaeli pair of. adjacent `.plates '5 .presentsaihigninipedance to the flow o'f current iro'mone plate `vto the other.As aresult of. this action, cnrrent...is. eiectiyely prevented fromlowilngl Yin thev wall '.1 of theant'ennaA or any of thepl'ates 3.Thereforasubstantially zero coupling .appears between the antennasiAand'. B. l .It is found in practice that the. intermediat plates 9between. the -rst and l'ast plate.I may be omitted, leaving. only theirst plate 95 adjacent the Wall `I ofthe antenna A and the last plate:`9 adjacent. .the Wall .5. of the. antenna. Withoutv serinuslyaffectingthe deg-ree of isolation provided. Althougnthe inventionliasbeendescribed ywith reference to a specic type of'antenna system, it ,tobe. understood that its. usev is not limited, 'to antennas of the. typeshown,l nor tofantennasf-employing, parabolic .reflectorsv It will beclear to those,.skilled1inl the. .art W-itlioul'.I further discuslofall' of the conductors connected together. to

cause operation as short-circuited quarter wave lines.vr

1 A.Ref'erring, to:Figure 3,.. an-v effect simi-lar izo-that provided bythe plates 9 of Figure 1 may be secured bymeans of a plurality ofquarter-Wave rods `I3 connected atpoint's 'I5 alongfa conductor l1 l'Thepoints |15 are. spaced at. intervals. substantially less. .than.one-.quarter Wave1ength,and

cooperate in pairs as short-circuited open-'wire quarter wavey lines.

Referring to Figure 4, a further modification of the invention comprisesa plurality of parallel conductive discs I9, connected at their centersto points 2l on the conductor I1. In order to provide high impedanceresonance between the adjacent discs i9, the radii ofthe discs are notnecessarily one-quarter Wavelength, because each pair of discs acts as aradial parallel conductor line, with tapered constants, that is thecapacitance per unit length is largest at the outer end,- graduallydecreasing as the inner end is approached. Denoting the radius of theconductor Il as a and the radius of each discs I9 as b, a and b must beso related that:

2 b 2 2 l 2 b- J1 i K e=^ eKe Where A is the wavelength, Jo() is theBessel function of the first'klnd and and first order. l

I claim as my invention:

1. In a system including two antennas, ap-` paratus for preventingdirect-path transmission between said two antennas including a pluralityVof screens of conductive material each having substantially parallelfront andback edges, and

each substantially one-quarter wavelength wide from front to back, andmeans supporting said screens in spaced planes perpendicular to the linebetween said antennas, said supporting means comprising a conductorextending generally parallel to said line and connected to each of saidscreens at its back edge. 2. In a system including two antennas,apparatus for preventing'directfpath transmission between said twoantennas including la plurality of discs of conductive material disposedin spaced planes perpendicular to the line between said antennas, and aconductor extending generally parallel to said line and connected toeach of said discs. j y

3. In a system including two antennas, apparatus for preventingdirect-path transmission rbetween said two antennas including aplurality of discs of conductive material disposed in spaced 'planesperpendicular to the line between said antennas, and a conductorextending generally parallel to said line and connected to each of saiddiscs, the radius a of saidconductor being related to the radius b ofeach of said discs by the equation:

Jrerfocaarmffra y and 4. In a system including two antennas, apparatusfor preventing direct-path transmission between said two antennasincluding a plurality of discs of conductive material disposed in spaced4 planes perpendicular to the line between said antennas, and aconductor extending generally parallel to said line and connected toeach of said discs, the diameters of said conductor and said discs beingsuch that the radial distance from the edge of each disc to the point ofconnection of said disc to said conductor lies between one quarter'wavelength and one eighth wavelength at the lowest frequency at whichsaid antennas are series resonant.

5. In a system including two antennas, apparatus for .preventingdirect-path transmission `between said two antennas, including aplurality of parallel-conductor transmission line sections,

means supporting said line sections between said antennas andperpendicular to the line between -said antennas, said supporting meansshortcircuiting each of said line sections at least at one point thereonto provide high impedance paths between said antennas.

6. In a system including two antennas, apparatus for preventingdirect-path transmission between said two antennas, including aplurality of plates of conductive material each having sub-l stantiallyparallel front and hack edges, and each substantially one-quarterwavelength wide from front to back, and means supporting said plates inspaced planes perpendicular to the line between said antennas, saidsupporting means comprising a sheet of conductive material secured tosaid back edges only of said plates.

' 7. In a system including two antennas,` apparatus for preventingdirect-path transmission between said two antennas including a pluralityof substantially flat bodies of conductive material each having a frontedge and a back edge and each substantially one-quarter wavelength widefrom front to back, and means supporting said bodies in spaced planesperpendicular to the line between said antennas, said supporting meanscomprising a conductor extending generally parallel to said line,connected to each of said bodies at its back edge.

.8. In a system including two antennas, apparatus for preventingdirect-path transmission between said two antennas, including aplurality of bodies of conductive material each having substantiallyparallel front and back edges and each substantially one-quarterwavelength wide from front to back, and means supporting said bodies inspaced planes perpendicular to the linebetween said antennas, saidsupporting means comprising a conductor extending generally parallel tosaid line, connected to each of said bodies at a point one-quarterwavelength distant at its back edge only. i

9. In a system including two antennas, apparatus for preventingdirect-path transmission between said two antennas, including aplurality of bodies of conductive material each having substantiallyparallel front and back edges and each substantially one-quarterwavelength wide from front to back, and means supporting said bodies inplanes perpendicular to the line between said antennas, at intervals ofapproximately onetenth wavelength at the frequency at which the systemis to operate, said supporting means comprising a conductor extendingsubstantially parallel to said line, connected to each of said bodies atits back edge. 10. An antenna system( comprising two antennas spacedfrom each other, a sheet of conductive material disposed substantiallyin a plane parallel to the line between said antennas, and a pluralityof plates of conductive material each 5 6 having substantially front andback edges and REFERENCES vCITED dlsposed m planes perpendlcular to SaidIme at The following references are of record in the intervals ofsubstantially less than one-quarter ,Y wave-length at the lowestfrequency at which said me of this patent' antennas are series resonant,each having its back 5 UNITED STATES PATENTS edges only connected tosaid sheet. Number 11. The invention as set forth in claim 1o, 2261 272,Newe Novntelgu wherein each of said plates is substantially one-2275312 Tuniek "Feb '10 1942 quarter Wavelength long from front to backat 231:196 Lindenb: Apr: 28 i942 the lowest frequency at which saidantennas are 10 series resonant.

GEORGE H.'BROWN.

